Thunder Tiger Decathlon - Construction Article

The Decathlon has been a staple in the aerobatics world of “Big” aircraft for a long time and has been used to teach many to gain their aerobatic endorsement on the Private Pilots License PPL.

 On open up the groovy box, I was presented with a multitude of components that had all been well packed. Two wings halves wrapped in Plastic and protected by thin foam sheeting. The fuselage in its sectioned off part of the box, also wrapped in plastic and the rest of the various components stored in cardboard boxes.  

After ten minutes of struggling with the packaging, there laid out in front of me was the basis of a Super Decathlon, in a splendid shade of Yellow and Blue.  

The fuselage is easily assembled, the instruction are clear and concise, with no errors.

Hardware

The quality of the hardware is pretty good and unless you are really finicky, I could find no reason to change it. 

 Power

An OS Max 40FP was installed upfront with a 10.5 x 6 Bolly to start with. The engine was mounted on the standard engine mounts supplied with the Kit. I did however dump the engine mounting screws supplied for Dubro Engine Mount Screws, as these have served me well in the past.  I also installed a Fuel Filter just to make sure the fuel gremlins don’t get me. After installing the engine the cowl was cut as outlined but the instruction in the manual.

Radio

I installed a mixture of Hitec Servos, HS422 on the Ailerons and HS311 for the Rudder, Elevator and Throttle. The reciever was a Hitec Micro 555 5ch and a 1100mah battery pack provided the juice. This was all was controlled by a Hitec Flash 5 SX Radio.

The Final Setup  

The ailerons are the usual mount the servo in the wing and hook up to the aileron directly via a wire pushrod and nylon clevis / control horn.

The elevators are a little different, in that the elevator is two pieces and has a single pushrod, which is comprised of a long section of hardwood dowel, with a single piece of piano wire at one end and dual pieces of piano wire at the other end. The single piece is connected to the servo and the dual pieces are both individually connected to each half of the elevator.

 A small word or caution here, make sure you set this up correctly, otherwise you will have an aircraft that will like to roll a certain way. The elevator halves need to be set so that they are inline with each other. This is not difficult as each side has its own adjustable nylon clevis, so take your time and get it right.

 The Rudder is a PULL PULL system, this is a little fiddly to setup, but it is worth the effort as the control is positive and low drag for the servo.

 The throttle is controlled by a single pushrod, which passes through the firewall. All control throws were set as per the manual’s suggestions.

 Set the balance as per the instructions in the manual, it makes the aircraft quite stable. After you have done your test flights you can play around with it to make the aircraft more aerobatic or more stable, which ever you prefer. Mine balanced perfectly with the 40FP in the nose, I needed no additonal weight. The total all up weight of mine was 3kg, the manual states between 2.5 and 3 kg, so I was in the ballpark.

 I also make a habit of going over the whole airframe as the last thing I do to check that all bolts and screws are tight and also to check I did not forget anything. This has paid off many times.

At the field

So the day had come to take the Decathlon to the field for its first flight. At the field it was a little breezy, but a fine, clear day. After getting through the normal pre-fligth / first flight checks, the Decathlon was lined up on the runway.

The take off was a little eventful and it almost did not make it cleanly from the ground. During the runup roll I applied a little rudder to correct the yaw. What I thought was a little, it thougth was a lot. Next thing you know I am going from one side of the runway to the other and it almost ended in tears. Evetually I got it undercontrol and up into the big blue.

After landing I checked the rudder throws and they were larger than reccomended. I adjusted them back to reccomended setting and lined up again.

Once airborne, without the theatrics of the previous takeoff,  a few slight adjustments were made to trims, to get it flying straight.  

During this flight I took time to notice the general tracking of the aircraft and its handing, without doing any heavy aerobatics. In general it handles pretty well, there is considerable roll coupling with the use of the rudder.  

Come in to land and it just floats, but is quite stable and settles into a nice flare and then lightly kisses the ground. Taxi back to the pits and have a bit of a gecko to see how things are, I generally retighten every nut and bolt after the second flight just to make sure. Nothing was loose and the overall inspection was good, with one exception, the Wheel Spats.

 These had been chipped/cracked, but not because of contact with the ground. There was not a mark on them and this left me puzzled. After a good look and a bit of a head scratching, I found the culprit. The pieces of ply, that are supplied to support the fibreglass shell of the spat and that also provide an anchor point for the mounting screw, are too small.

 They do not support the whole side of the spat and during the take off and landing roll, the vibration of the wheel in the rough ground caused the spat to vibrate badly. This vibration caused the gel coat to crack away in pieces around the standard ply support. This is a small thing, but probably needs some looking at by the manufacturer. After I returned home I replaced the small pieces with larger pieces and the spat is a lot more stable. 

 Loops are a joy, quite large on low rate, but nice and tight on high rates. As previously stated the rudder has considerable power and also considerable roll coupling. So you can make it perform a rudder roll very easily, you will have to chase it a little with the elevator. Knife edges are possible, but you really need to add considerable aileron to compensate. Once you get this sorted out, it is quite a lot of fun.  

Stall Turns, Tail Slides, Humpty Bumps, Cuban Eights, you name it, it does it and all in a scale manner.

 Summary

All in all this is a nice looking and flying aircraft. It is a little different to look at than the ever popular Piper Cub, but has similary flight characteristics, just hotter.

 This aircraft is sound flyer, with no bad habits. It is stable and handles a lot like a Piper Cub, but when pushed with enough power, it will really burn up the sky.

 Thunder Tiger have really delivered a package that has the ability on low rates to be a superb trainer, but when high rates are added and the throttle is pushed past the middle of its throw, you will find your self having a lot of fun.